I have just purchased a Lumia 950, really happy it except the screen goes black when I am calling or receiving calls. I put a tempered glass screen protector on the device on Saturday but this has made no difference...

I have just purchased a Lumia 950, really happy it except the screen goes black when I am calling or receiving calls. I put a tempered glass screen protector on the device on Saturday but this has made no difference...

You didn't make any update? there's a firmware update (hope you Don't own a AT&T or t-Mobile), that could be a proximity sensor iussue and update should fix it. Are you sure you didn't cover the upper front side of phone?